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Exercise 8: Disease Management with Integrated Tactics
We have looked at various late blight management tactics individually and have observed their impact
on a late blight epidemic. Now let's look at how they can be integrated into an overall program
of late blight management. Let us begin with a "worst case" scenario and add a disease management tactic
one at a time. After every simulation, copy and paste the economic report into a document in a text
editor for later analysis and comparison.
- Uncontrolled epidemic. Set the initial values for the variables as follows:
- Potato, Resistance Level: low
- Environment, Weather: cool, wet
- Inoculum, Sporangia, Cull pile: 1000 sporangia/day, 10 meters from field
- Inoculum, Infections, Infected seed: 100 infections/ha
- Inoculum, Infections, Volunteers: 50 infections/ha
- Fungicide Spray. Apply a single systemic fungicide spray on July 13. Although it reduces
the rate of epidemic development somewhat, clearly by itself a single spray of the systemic
fungicide is not adequate to control the epidemic under these conditions.
- Partial resistance. In the Potato menu, change the Resistance Level from
"low" to "moderate." Run it first without any fungicide spray, and then apply the systemic fungicide
on July 13 as before.
- Moving the cull pile. In the Inoculum menu, select Sporangia..., and change
the distance of the cull pile from the field from 10 meters to 100 meters.
Apply the systemic fungicide on July 13 as before.
- Removal of volunteers. In the Inoculum menu, select Infections..., and
change "Volunteers" from 50 to 0.5 infections/ha. Apply the systemic fungicide on July 13
as before. How much would you be willing to invest in labor to remove volunteers?
- Certified Seed. In the Inoculum menu, select Infections..., and change
"Infected Seed" from 100 to 0.1 infections/ha. Apply the systemic fungicide on July 13
as before. In the economic report, pay particular attention to the net profit. Is the
price premium that you have to pay for certified seed ($313/hectare) economically justified for
the control of late blight? Economically speaking, how would you account for certified seed?
The same level of disease control could be achieved with fungicides alone. Reset the initial values
of the variables to those of the "worst case" scenario in step 1 above. Run the simulation applying
as many sprays of the protectant or systemic fungicide (or any combination of the two) to achieve
approximately the same final level of disease that you got in step 6 above. Which approach would you
prefer? Why?
....return to Introduction
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